Cathode-ray tube



p 1952 c. s. SZEGHO ET AL 2,612,611

CATHODE-RAY TUBE Filed June 25, 1950 Fig.1

Least Resolvoble Sepurufion- CONSTANTIN S. SZEGHO Thickness 1 MARK E. AMDURSKY IN V EN TORS.

THEIR ATTORNEY Patented Sept. 30, 1952 UNITED STATES PATENT O FICE-g 1 f I 2;e1z:s11"- f I I CATHODE-RAY: TUBE! Constantin S; S'zeglio and. Mark E.Amdursky, Chicago, 111;, .assign'ors to The'Razuland" comrration; acorporation of Illinois" I Application-June23, 1950;. Serial.No.= teases 'This. invention relates. to image-reproducing "devices? and more. particularly to. such devices ished'surf'ace ofithei viewing plate of'a presentday picture tubeis asource.offundesirablespecular reflection,,to suchan extent that external light from'fl'oor lampsand the like produces a specular image which detracts from the quality of the reproduced picture. It hasrbeen suggested that undesirable. specular reflection may be reduced by coatingthe glass viewing plate. with a plastic light-diffusing substance but while this scheme has materially reduced. the amount. of specular reflection, it has beeniound. that such a plastic coating isnot sufficiently rugged. and

durable to warrant its use on a commercial basis. It is also known that glare. fromia glass article, caused by reflection of externalli'ght, may bereducedb'y providing .thesurfaceoflthe article with I a' skeletonized' coating of substantially one-quarter'. wavelengthin thickness; this expedient. is:

impracticalior application to a .televis'ionpicture tube because such a. skeletoni'zedcoating .is colcrthe selective to reflected light; Moreover, schemes knownt'o the'prior art fer reducing glare have" also been foun'dto-causesuch aireduction zclaimsz (c1. 250 -36) inpicture resolution as: to mak'ethem unacceptable for. general use.

In thecopending application of Constantin S.-

Szegho et all, SerialTNo'. 169,998, filed concurrently ternal-suriaceofthe glass viewing plate is ma.-- teri-allyreduced by relieving,.or placing inrelief,

the. outer surface ofv the viewing plate. Asset forth. inthe copending application, it has been fdund'that in this manner, under certain conditions,v a material reduction in g-laremay be achieved withoutlappreciabl'e loss; in picture detail. However,, specular reflection of external lightfiirom theinner surface of the faceplatemay. still he observed, andwhile. this: reflection 2 I I without excessive lcss. of.- picture definition, f a rather careful. control must' be maintained throughoutltheprocessing;oflthe face plate. It is a primary object ioflthepresent invention to. provide. a. new and I improved image-reproduce ing. device which afiords. the. advantages. of the device described .in, the above identi'fied' copending. application. while. substantiallyfreducingi or eliminating. specular. reflection from the. inner surface.ofithe glass=viewi'nglplata, I

'It'is aiurtherobj'ectLoi.theinventiontoprovide av new and improved. cathode-rayipictiire tub'efiii which a greater. decrease; specular reflection of external light is. obtained while, at'lthe same time, better picture resolution is; achieved than" withnthei deviceofl the icoperiding. application, Animage-reproducing device constructed in accordancewwitlitheipresentinvention. comprises a glass viewing. plate. having. relieved inner and" outersurfacesand'a-fluorescent screen supported adjacent the inner surface. of the viewing. plate. Preferably, the relievedinner and-outer surfaces. eachncomprise a multitude offmicroscopicl nod'u-' lar protub'erances. individually; of. from 51"to I0" microns in. height and' from 251to1'00microns in: diameter. Such a. glass. vi'ewingplate is. char.. acterized .by areflectivit'y measured'at an angle ofrrefiection substantially equal'lto. the angleofincidence. of avlcollimated beam. of light directed. at the outer surface of'thel viewing, plate at an angleoffiisubstantially 851 degrees from normal; within the rangefro-m OLE-per cent to 2Iper' centi I-I that ofiamirrorrsurface; I

The featuresof thepresent invention which. are

I believed tobenovelare setforth with particularity in..the. appended'. claims. The. invention,,to- I gether. with further, olsiject's and advantages thereof, may best. be? understood;howevergby reference to,..the following description taken in connection with thei accompanying-t drawing, in the. several. figures of which like" reference n'ue merals indicate like elements; and injwhich:

Figure his a fragmentaryJside-elevational view, partly. in sectiomof an'iin'age-reproducingdevice constructed'lin accordance with 'the'inventiom.

I Figure zii'sia plan view. greatly enlarged}.of'aI portionof .theglassiviewing plate oflthe device of Figure. 1' as seenunderamicroscopm.

isjnotas. seriousas. that obviated by, relieving the outersurface, it nevertheless detracts-to some extentfrom the-picture-quality. Moreover; in

orderito-obtain the maximum reduction in glare:

Figurel3i is a crossrsecticnal-viewtaken alcngi theline 3 -'3'-.of.Fi'gure2; Iand 1 v ,F -ig-urev 4.'is.a graphicalfrepresentation useful in understandingjtheinventiom. I I IqI Thecathode-ray picturestubetof lfiig-ure L comaprises:aglasswenvelope: Iii; having a-glass vi ewing plate I l r adJ acent .theeinnenqsurface ofMhichds:

nection of conductive coating l3 in an-external' circuit.

The image-reproducing deviceof Figure 1 is entirely conventionalin allrspects with the exception of the construction of glass viewing plate H. In accordance with the invention, both the inner and outer surfaces of the viewing plate II are relieved, or placed in relief, by being provided with a multitude "of microscopic nodular protuberances, in order to reduce the reflectivity Oftheiviewingplate? The appearance to the naked eye'of the face plate constructed in accordance with the invention is smooth andsomewhat cloudy,but not's-o cloudy astjo be opaque; However, when-viewed under a high-powered microscope, a rathe -"unif -orm distributionof minute,

convexor. nodularhills; or protuberances may .be discerned, as shown inFigure's 2 and 3. e

As set forthin the above identified copending application, relieving the outer surface effects a substantial reduction inflspecular reflection or glare from external light while maintaining the picture definition within acceptable limits. In'. accordance with the present invention, the inner surface, as'well as'the outer; surface, is'relieved, with two very importantadvantages. In the first place, sp'ecular reflection from the inner surface of the viewing 'plate,' still observable when only the outer surface is relieved, may be substantially eliminated. Moreover, by relievingiboth inner,

and outer surfaces, the heightof the individual nodulesmay be decreased and the diameter in creased, with, the result that a greater decrease of specular reflection may be obtained with a smaller sacrifice in picture detail.

'Ihusfinaccordance with the present inven tion,it has been found that if'the microscopic nodular protuberances on the outer and inner surfaces of glass plate H are individually within therange frm tolO microns in height and from 25 170100 microns in diameter, the sacrifice in picture detail is so slight as to be completely unnoticeable. ',Such a viewing plate is', capable of resolving-at least-2.2 lines per millimeter, I which corresponds 130 4.5 PQIEl/fl'SlOIlliIlES per mil cceptable in accordance limeter and is quitefa with present'television practice.

At the same time, however, the reflectivity with respect to light from external sources is materially reduced; As measured with respect to a' collimatedbeam oflight'directed at the external surface of the viewing plate at an angle ofsubstantially 35 degrees from normal incidence, the

reflectivity (that measured at an angle 01" reflection equal to the angle of incidence) of a cathode-- ray tube viewing plate 'constructedin accordance with the invention'hasibe'en: found to lie within the range'from 0.5 per cent to 2 per cent of that of a mirror siu'face or perfect reflector, as loompared to a figure'of substantially '7 pericent for a tube havinga polishedneutral-tinted filter face plate of approximately 66% transmission, or

about seer cent fora tube having-a clear window glass face 'platel Moreover, it has been found reduction in reflectivity.

that the picture definition is correlated with the reflectivity, so that all face plates which exhibit diffuse reflection and which have a reflectivity within the specified range are acceptable as regards picture detail, while those lying outside the specified range are characterized either by too great a loss of ,picture detail or by an insufficient The desired surface condition may be achieved in accordance with any of a number of processes. For example, the outer and inner surfaces of the viewing plate may each be roughened by liquid honing or vapor blasting, after which the surfaces are subjected to the chemical action of hydrofiuorioacid until a reflectivity within the specified range is obtained. This process is specifically disclosed and claimed in the copending application of Constantine S. Szegho et 9.1., Serial No. 169,998, filed concurrently herewith, for Process for Producing Low-Glare Cathode- Ray Tube Viewing Plates, assigned to the present assignee. Another process which has been suc-,

cessfully employed comprises the steps of frost etching the outer and inner surfaces (with a com mercial frost. etch composition comprising ammonium .bifiuoride as an active ingredient) to render the surfaces matte, and subsequently etching with hydrofluoric acid. Still another process which may be employed comprises the steps of fusing a ceramic frit into the outer and inner surfaces of the viewing plate and subsequently etching with hydrofluoric acid until a reflectivity within the specified range is obtained. Whatever the processused, it has been found that whenever the face plate exhibits diffuse reflection and the reflectivity falls within the range specified above, the loss of picture definition is so smallas to'be negligible. When the reflectivity is below the range specified, the loss of picture detail is excessive, while reflectivities above the specified range do not provide a sufiicientreduction in glare to warrant the expense of the process.

It has also been found that, for any given value of reflectivity, the picture definition is substantially in an inverse linear function of the face plate thickness. illustrated in Figure 4, in which the least resolvable separation is plotted as a function of the.

thickness of the viewing plate, reflectivity being maintained constant. Thus it is apparent that, for a predetermined picture definition, higher reflectivities are required for thicker face plates.

Glass-bulb cathode-ray tubes are characterized f by a variation in face plate thickness, the viewing plate having an appreciably greater thickness at the periphery than at the center. Accordingly,

in order toobtain acceptable picture definition at the edgesof the screen, it is necessary to provide a higher reflectivity than would be necessary if only the center of the screen were to be considered. The ranges specified for reflectivity, and for the height and diameter of the individual microscopic nodules appearing on the viewing plate surface, are those which have been found acceptable for use in connection with glass-bulb cathode-ray picture tubes. More narrow limits may be maintained inthe production of metalcone tubes, sincefthe quality of the glass used the viewing plate is better and more uniform; and since the viewing plate thickness is generally" less and more constant, than in the case of the glass-bulb tubes. Thus; the reflectivity of theviewing plate ofa'metal-cone tube constructed in accordance-With the invention may be main This relationship is graphically tained within the range from 0.5 per cent to 1.5 per cent of that of a mirror surface, thereby permitting greater uniformity in production and a greater reduction in glare. In order to obtain reflectivity readings Within this latter range, it has been found that the microscopic nodular protuberances on the surface must be from 5 to 10 microns in height and from 25 to 59 microns in diameter.

Thus, the present invention provides a new and improved image-reproducing device, and more particularly a novel cathode-ray picture tube, which affords a substantial reduction in glare from external light sources without materially sacrificing picture detail. The correlation between refiectivity and picture definition which has been observed appears to hold without reard for the process with which the viewing plate is treated. This finding facilitate large scale inspection of the treated tubes to determine in advance whether or not the required picture resolution may be obtained.

While particular embodiments of the present invention have been shown and described, it is apparent that various changes and modifications may be made, and it is therefore contemplated in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

We claim:

1. An image-reproducing device comprising: a glass viewing plate having relieved integral inner and outer surfaces each comprising a multitude of microscopic nodular protuberances individually of from 5 to 10 microns in height and from 25 to 100 microns in diameter; and a fluorescent screen supported adjacent said inner surface.

CON STANTIN S. SZEGHO. MARK E. 'AMDURSKY.

REFERENCES CITED.

The following references are of record in the file of this patent:

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Burroughs Oct. 25, 1949 

